I have retested after uninstalling and reinstalling the driver and the issue remains. Although games and bandicam report ~60fps the MP4 output varies between 30-45fps.
Running the same test on OBS achieves a steady ~60fps.
Since 1 May (or thereabouts), although in-game FPS and the Bandicam FPS overlay both show 60+ FPS, the MP4 output files are ranging from 30-45 fps. I checked older recording, and they are definitely ~60fps. I've recorded over 800 videos. I am confident I know what I am looking at. I have just update...